Distichiasis

If you notice your dog squinting and pawing at its eyes, or if the eyes are red, inflamed and watering heavily, a trip to the veterinarian is in order. It's possible in this case that your dog may have distichiasis, a condition that occurs when the eyelashes grow abnormally, placing them in direct contact with sensitive eyeball tissue. The hairs are often long and stiff and grow out of oil glands within the eyelids. In most cases there are multiple improperly grown hairs, and both eyes are affected. Also, even though dogs usually have no lower eyelashes, in cases of distichiasis both lower and upper eyelids can be affected. [...]

In a normal canine eyelid structure, hairs called eyelashes grow forth from the rim of the eyelid, pointing outward, and are used much like bronchial cilia to trap dust and foreign bodies from entering the sensitive membrane of the eye. There are, however, instances where this goes wrong, and it usually manifests in one of three ways. Ectopic cilia, when the eyelash grows through from the outside to the inside of the eyelid; trichiasis, which eyelashes start growing normally but turn inward; and the most severe: distichiasis, when hairs begin growing from the inside of the eyelid pointed towards the eye. In special circumstances, distichiasis is compounded with a secondary symptom called narrow palpebral fissure in which the opening afforded by a dog's eyelid is significantly smaller than normal. When this happens, it makes treatment especially problematic, and thus it's this compound problem that this article concerns itself with. [...]